Lasers have been used in many firearms applications as tools to enhance targeting. For example, one form of firearm sight makes use of a laser placed on a handgun or a rifle and aligned to emit a beam parallel to the barrel. Since a laser beam by definition has low divergence, the laser light appears as a small spot even at long distances. The user places the spot on the desired target and the barrel of the gun is aligned (but not necessarily allowing for bullet drop or movement of the target while the bullet travels).
Most laser sights use a red laser diode. Others use an infrared diode to produce a dot invisible to the naked human eye but detectable with night vision devices. Many sights can be calibrated in order to precisely align them with the barrel of the firearm. However, it is difficult to calibrate (e.g., “sight”) an infrared laser due to the need for special infrared vision gear, and the procedure cannot be carried in daylight. Furthermore, dual red/infrared sights must be sighted twice: once to align the red laser diode and a second time to align the infrared laser diode.
Additional problems with laser sights is that they can render the firearm incompatible with a holster, they can be awkward to use, and activation of the sight can require grip changes that interfere with quick and effective shooting procedures.